
#ifndef __substitute_h__
#define __substitute_h__

#include "yacasbase.h"
#include "lispobject.h"


/** Behaviour for substituting sub-expressions.
 */
class SubstBehaviourBase : public YacasBase
{
public:
    virtual LispBoolean Matches(LispPtr& aResult, LispPtr& aElement) = 0;
};

/** main routine that can perform substituting of expressions
 */
void InternalSubstitute(LispPtr& aTarget, LispPtr& aSource,
                        SubstBehaviourBase& aBehaviour);


/** Substing one expression for another. The simplest form
 * of substitution
 */
class SubstBehaviour : public SubstBehaviourBase
{
public:
    SubstBehaviour(LispEnvironment& aEnvironment,LispPtr& aToMatch,
                  LispPtr& aToReplaceWith);
    virtual LispBoolean Matches(LispPtr& aResult, LispPtr& aElement);
private:
    LispEnvironment& iEnvironment;
    LispPtr& iToMatch;
    LispPtr& iToReplaceWith;
};

/** subst behaviour for changing the local variables to have unique
 * names.
 */
class LocalSymbolBehaviour : public SubstBehaviourBase
{
public:
    LocalSymbolBehaviour(LispStringPtr* aOriginalNames,
                         LispStringPtr* aNewNames, LispInt aNrNames);
    virtual LispBoolean Matches(LispPtr& aResult, LispPtr& aElement);
private:
    LispStringPtr* iOriginalNames;
    LispStringPtr* iNewNames;
    LispInt iNrNames;
};

/** subst behaviour for backquote mechanism as in LISP.
 * When typing `(...) all occurrences of @a will be
 * replaced with:
 * 1) a evaluated if a is an atom
 * 2) function call with function name replaced by evaluated
 *    head of function if a is a function. For instance, if
 *    a is f(x) and f is g, then f(x) gets replaced by g(x)
 */
class BackQuoteBehaviour : public SubstBehaviourBase
{
public:
    BackQuoteBehaviour(LispEnvironment& aEnvironment)
        : iEnvironment(aEnvironment) {};
    virtual LispBoolean Matches(LispPtr& aResult, LispPtr& aElement);
    LispEnvironment& iEnvironment;
};




#endif

